Catheter with liquid-cooled control handle

ABSTRACT

An electrophysiologic catheter with an improved control handle is provided. The catheter includes a heat transfer assembly to better dissipate heat in the control handle. The heat transfer assembly includes a pump, a reservoir containing a coolant, a heat transfer member, and a coolant transport network transporting coolant between at least the reservoir and the heat transfer member. In one embodiment, the heat transfer member is located within the control handle as a heat exchanger on the circuit board to receive the coolant for transferring heat from the integrated circuits to the coolant. In another embodiment, the heat transfer member is located on the circuit board directly surrounding the integrated circuits to internally cool the integrated circuit within the control handle. A second heat transfer member is located outside of the control handle as a heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of, and claims priority to and thebenefit of, U.S. application Ser. No. 14/666,247 filed Mar. 23, 2015,now U.S. Pat. No. 9,289,259, which is a continuation of, and claimspriority to and the benefit of, U.S. patent application Ser. No.12/942,880 filed Nov. 9, 2010, now U.S. Pat. No. 8,986,303, the entirecontents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to catheters and, in particular, to acatheter with an improved control handle.

FIELD OF INVENTION

Catheters have been in common use in medical practice for many years.Applications of catheters include stimulating and mapping electricalactivity in the heart and ablating sites of aberrant electricalactivity. Such catheters are also referred to as electrode catheters. Inuse, an electrode catheter is inserted into a major vein or artery,e.g., femoral artery, and then guided into the location of interestwithin the body, e.g., the chamber of the heart where aberrantelectrical activity within the heart is located.

A typical ablation procedure involves the insertion of a catheter havinga tip electrode at its distal end into a heart chamber. A referenceelectrode is provided, generally taped to the skin of the patient. RF(radio frequency) current is applied to the tip electrode, and currentflows through the media that surrounds it, i.e., blood and tissue,toward the reference electrode. The distribution of current depends onthe amount of electrode surface in contact with the tissue as comparedto blood, which has a higher conductivity than the tissue. Heating ofthe tissue occurs due to its electrical resistance. The tissue is heatedsufficiently to cause cellular destruction in the cardiac tissueresulting in formation of a lesion within the cardiac tissue which iselectrically non-conductive. Lesions created by such cardiac ablationprocedure effectively interrupt errant electrical pathways in the heart.

Catheters typically have an elongated catheter body, a deflectablesection distal the catheter body and tip section distal the deflectablesection. A typical ablation catheter provides irrigation at the tipelectrode for a number of reasons, including the avoidance of charringand the desire for larger lesions. By irrigating the ablation electrode,such as with room temperature physiologic saline, the ablation electrodeis actively cooled instead of more passive physiological cooling byblood flow. Because the strength of the RF current is no longer limitedby the interface temperature, current can be increased for larger andmore spherical lesions.

A control handle proximal the catheter body serves primarily to housedeflection mechanism coupled to puller wires extending through catheterand provide an interface by which a user can manipulate the deflectionmechanism. Where irrigation is provided, an irrigation tubing extendsthrough the control handle to pass fluid from a fluid source to a distalend of the catheter. The control handle also normally houses a printedcircuit board supporting various circuits and chips configured forsignal processing from and/or to the distal section or tip electrode,including, for example, amplification of signals from an electromagneticposition sensor and/or digitizing circuits for digitizing a voltagesignal of the thermocouple. An EPROM chip may also be included to shutdown the circuit board after the catheter has been used so as to preventreuse of the catheter, or at least the electromagnetic sensor.

Current catheters with a control handle containing a PC board rely onnatural convection within a closed chamber of the control handle toprovide cooling of the PC board. As catheters become more advanced andcapable, the internal electronics become more involved, often resultingin greater thermal waste energy loads. Increases in thermal wasterenergy result in increased thermal temperatures in the control handleand ultimately high handle temperatures which can negatively affect usercomfort.

Small fans are often used on PC boards to increase the convective heatloss of the board. However, because control handles are typicallysealed, the heat load will increase the handle temperature. In order forfans to be effective in a catheter handle, inlet and outlet grates orports should be integrated into the catheter handle. But such featuresmay diminish the aesthetics of the handle. Heat pipes can also beintegrated into the handle to increase heat transfer from the mountedintegrated circuits, but again the heat will tend to remain in thehandle increasing handle temperature. Self pumping micro fluidic heatexchangers may also be used but, like heat pipes, they will release heatenergy into the handle resulting in increased handle temperatures.

As irrigation fluid at room temperature ranges between about 20-25 C (or68-77 F), which is significantly lower than the normal human bodytemperature of 37 C (or 98.6 F), and it is known to pass irrigationfluid through the control handle, it would be desirable to provide animproved control handle that uses the irrigation fluid flowingtherethrough to help cool the PC board and lower the temperature insidethe control handle by transporting the heat out of the control handle.Such increased heat transfer will result in lower operating temperatureof the PC board and hence a cooler control handle.

SUMMARY

The present invention is directed to an electrophysiologic catheteradapted for use in a patient's heart with an improved control handle.Catheters typically have a catheter body and a control handle whichhouses a heat source, including integrated circuits mounted on a printedcircuit board, which can produce undesirable thermal waste energy loadsthat accumulate in the control handle causing discomfort to a user. Inaccordance with a feature of the present invention, the catheterincludes a heat transfer assembly to better dissipate heat in thecontrol handle. The heat transfer assembly includes a pump, a reservoircontaining a coolant, a heat transfer member, and a coolant transportnetwork transporting coolant between at least the reservoir and the heattransfer member. In one embodiment, the heat transfer member is locatedwithin the control handle as a heat exchanger on the circuit board toreceive the coolant for transferring heat from the integrated circuitsto the coolant. In another embodiment, at least one heat transfer memberis located on the circuit board directly surrounding the integratedcircuits to internally cool the integrated circuit within the controlhandle. A second heat transfer member is located outside of the controlhandle as a heat exchanger. The heat transfer member of this embodimentmay be an IC heat transfer unit, a cover heat transfer unit or a heattransfer assembly. Either embodiment may be configured with a closed acoolant transport network or an open coolant transport network.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and aspects of the present invention will be more apparentfrom the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a schematic diagram of a catheter, including a heat transferassembly, according to an embodiment of the present invention.

FIG. 2A is a side cross-sectional view of the catheter of FIG. 1,including a junction of a catheter body and an intermediate section,along a first diameter.

FIG. 2B is a side cross-sectional view of the catheter of FIG. 1,including a junction of a catheter body and an intermediate section,along a second diameter generally perpendicular to the first diameter.

FIG. 2C is an end cross-sectional view of the catheter of FIGS. 2A and2B, taken along line C-C.

FIG. 3 is a side cross-sectional view of the catheter of FIG. 1,including a junction between an intermediate section and a connectortubing, with a tip electrode.

FIG. 4 is a side cross-sectional view of the control handle of FIG. 1,including a piston with a thumb control.

FIG. 5 is a schematic diagram of a catheter, including a heat transferassembly, according to an alternate embodiment of the present invention.

FIG. 6 is an perspective view of a printed circuit board within acontrol handle of the catheter of FIG. 5, according to one embodiment ofthe present invention.

FIG. 7a is a side view of a heat transfer member in the form of an ICheat transfer unit of the present invention, according to oneembodiment.

FIG. 7b is a side view of a heat transfer member in the form of a coverheat transfer unit of the present invention, according to oneembodiment.

FIG. 7c is a side view of a heat transfer member in the form of a heattransfer assembly of the present invention, according to one embodiment.

FIG. 8 is a schematic of a catheter, including a heat transfer assembly,according to another alternate embodiment of the present invention.

FIG. 9 is a schematic of a catheter, including a heat transfer assembly,according to yet another alternate embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention will be described more fullyhereinafter, in which exemplary embodiments are shown. This disclosuremay, however, be embodied in many different forms and is not beconstrued as limited to the exemplary embodiments set forth herein.Here, when a first element is described as being coupled or connected toa second element, the first element may be directly connected to thesecond element or indirectly connected to the second element via one ormore third elements.

FIG. 1 illustrates a catheter 10 according to an embodiment of thepresent invention. The catheter 10 includes an elongated catheter shaftor body 12 having proximal and distal ends, an intermediate section 14with uni- or bi-directional deflection distal of the catheter shaft 12,a tip section 15 with a tip electrode 17 at a distal end of theintermediate section, and a control handle 16 at the proximal end of thecatheter shaft 12. Advantageously, the catheter includes a heat transferassembly employing a reservoir of coolant and a pump to provide coolingof integrated circuits housed in the control handle by means of forcedconvection.

As shown in FIGS. 2A and 2B, the catheter body 12 comprises an elongatedtubular construction having a single, axial or central lumen 19. Thecatheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 comprises an embedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 12 so that, when the control handle 16 is rotated, theintermediate section 14 of the catheter 10 is able to rotate in acorresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 9 french, more preferably about 7 french.Likewise, the thickness of the outer wall 20 is not critical, but isthin enough so that the central lumen 19 can accommodate puller wires,one or more lead wires, and any other desired wires, cables or tubes. Ifdesired, the inner surface of the outer wall 20 is lined with astiffening tube 21 to provide improved torsional stability. In oneembodiment, catheter 10 has an outer wall 20 with an outer diameter offrom about 0.090 inches to about 0.094 inches and an inner diameter offrom about 0.061 inches to about 0.065 inches.

The intermediate section 14 comprises a short section of tubing 22having multiple lumens, as also shown in FIG. 2C. In one embodiment, afirst lumen 30 carries one or more lead wires 50, temperature sensor(e.g., thermocouple wires 43 and 44) for monitoring tissue temperaturein the tip electrode 17, and a cable 74 for an electromagnetic position75 sensor housed in the tip section 14. A second lumen 32 carries apuller wire for at least deflection along one direction in a plane. Anopposing third lumen 34 can carry a second puller wire if bi-directionaldeflection along a second, opposing direction in the plane of the firstdeflection is desired. A fourth lumen 35 carries an irrigation tube 61for supplying fluid to the tip electrode. The tubing 22 is made of asuitable non-toxic material that is preferably more flexible than thecatheter body 12. In one embodiment, the tubing 22 is braidedpolyurethane, i.e., polyurethane with an embedded mesh of braidedstainless steel or the like. The number of lumens or the size of eachlumen is not critical, but is sufficient to house the lead wires, pullerwire(s), electromagnetic sensor cable, thermocouple wires and/orirrigation tubing depending on the embodiment.

A preferred means for attaching the catheter body 12 to the intermediatesection 14 is illustrated in FIGS. 2A and 2B. The proximal end of theintermediate section 14 comprises an outer circumferential notch 26 thatreceives the inner surface of the outer wall 20 of the catheter body 12.The intermediate section 14 and catheter body 12 are attached by glue orthe like.

If desired, a spacer (not shown) can be located within the catheter body12 between the distal end of the stiffening tube 21 and the proximal endof the intermediate section 14. The spacer provides a transition inflexibility at the junction of the catheter body and intermediatesection, which allows the junction to bend smoothly without folding orkinking. A catheter having such a spacer is described in U.S. Pat. No.5,964,757, the entire disclosure of which is incorporated herein byreference.

As illustrated in FIG. 3, the tip section 15 includes the tip electrode17 which may be connected to the tubing 22 of the intermediate section14 by means of a single lumen connector tubing 23. The connector tubingprovides space for the electromagnetic position sensor 75 and thevarious components extending from the tubing 22 to reorient themselvesas needed for anchoring in the tip electrode 17. To that end, a distalsurface of the tip electrode is provided with blind holes. In thedisclosed embodiment, blind hole 61 is provided to receive a distal endof the tip electrode lead wire 40, blind hole 63 to receive a distal endof the thermocouple wires 43 and 44, and blind hole 65 to receive adistal end of the electromagnetic sensor 75. Irrigation passage 66 isalso formed in the tip electrode to receive a distal end of theirrigation tubing 61. The passage 66 is in communication with transversebranches 67 and fluid ports 69 allowing fluid delivered through thetubing 61 to pass to outside of the tip electrode.

As shown in FIG. 2B, the puller wire 42 is provided for uni-directionaldeflection of the intermediate section 14. The puller wire 42 extendsthrough the catheter body 12, and is anchored at its proximal end to thecontrol handle 16, and at its distal end to the tubing 22 near thedistal end of the intermediate section 14 by means of a T-bar anchor 71,as generally described in U.S. Pat. Nos. 5,893,885 and 6,066,125, theentire disclosures of which are incorporated herein by reference. Thepuller wire is made of any suitable metal, such as stainless steel orNitinol, and are preferably coated with Teflon® or the like. The coatingimparts lubricity to the puller wire 42. The puller wire 42 preferablyhas a diameter ranging from about 0.006 to about 0.010 inch.

A compression coil 72 is situated within the catheter body 12 insurrounding relation to the puller wire 42, as shown in FIG. 2B. Thecompression coil 72 extends from the proximal end of the catheter body12 to the proximal end of the intermediate section 14. The compressioncoil is made of any suitable metal, preferably stainless steel and istightly wound on itself to provide flexibility, i.e., bending, but toresist compression. The inner diameter of the compression coil ispreferably slightly larger than the diameter of the puller wire. TheTeflon® coating on the puller wire allows it to slide freely within thecompression coil. The outer surface of the compression coil is coveredby a flexible, non-conductive sheath 78, e.g., made of polyimide tubing.

Longitudinal movement of the puller wire 42 relative to the catheterbody 12, which results in deflection of the intermediate section 14, isaccomplished by suitable manipulation of the control handle 16. Examplesof suitable control handles for use in the present invention aredisclosed in U.S. Pat. Nos. Re 34,502, 5,897,529, and 7,377,906, theentire disclosures of which are incorporated herein by reference. In theembodiment of FIG. 4, a distal end of the control handle 16 comprises apiston 54 with a thumb control 56 for manipulating the puller wire 42for uni-directional deflection of the intermediate section 14, althoughit is understood that the present invention is readily adaptable to acontrol handle with two puller wires for bi-directional deflection.

Connected to the piston 54 by means of a shrink sleeve 28 is theproximal end of the catheter body 12. The irrigation tubing 61, thepuller wire 42, the lead wire 40, the thermocouple wires 43 and 44 andthe electromagnetic sensor cable 74 extend proximally from the catheterbody through the piston 54. The puller wire 42 is anchored to an anchorpin 36 located proximal to the piston 54. The lead wire 40, thermocouplewires 43 and 44 and electromagnetic sensor cable 74 extend through afirst tunnel 58, located near the side of the control handle 16. Theelectromagnetic sensor cable 74 connects to a circuit board 64 in theproximal end of the control handle. Wires 73 connect the circuit board64 to, for example, a mapping and/or ablation system, including acomputer and imaging monitor (not shown).

Within the piston 54, the electromagnetic sensor cable 74 and lead wires40 are situated within a transfer tube 27 a, and the puller wire 42 issituated within another transfer tube 27 b to allow longitudinalmovement of the wire and cable near the glue joint 53. The irrigationtubing 61 extends proximally through the shrink sleeve 28 where itsproximal end is in communication with the heat transfer assembly 50 viaa distal conduit 68 a which extends through a second tunnel 60 situatednear the side of the piston 54 opposite the anchor pin 36.

The control handle 16 houses a heat source, including the printedcircuit (PC) board 64 on which are mounted multiple integrated circuitsserving various functions such as local amplification and/or processingof signals, including signals from the electromagnetic sensor and/or thethermocouple housed in the distal section of the catheter. An EPROM chipmay also be included to limit the catheter or at least the positionsensor to a single use.

In the embodiment of Figure, the heat transfer assembly 50 is configuredas an open system employing the reservoir 51 and the pump 52 (e.g., aninfusion pump), a coolant transport network with fluid conduits 68 a and68 b, and/or other mechanisms and components typically employed fordelivering fluid through the catheter to the tip electrode. As describedabove, irrigation fluid is delivered in the irrigation tubing 61 of thecatheter 10. In the present invention, the heat transfer assemblyadvantageously uses the fluid, e.g., irrigation saline, as a coolant tocool the PC board in the control handle. In the embodiment illustratedin FIG. 1, the infusion pump 52 pumps the fluid from the reservoir 51through the proximal fluid conduit 68 b passing into the control handle16. A distal end of the conduit 68 b terminates at and feeds into aninlet of a heat transfer unit, for example, a heat exchanger 90 (or heatsink) mounted on or near integrated circuits 80 on the PC board 64,especially high power output integrated circuits. An outlet of the heatexchanger feeds to a proximal end of the distal fluid conduit 68 a whosedistal end is in communication with a proximal end of the irrigationtubing 61 inside the piston 54. As shown in FIG. 4, the distal fluidconduit 68 a is anchored to the inside of the control handle 16 by gluejoint 53.

The heat transfer assembly 50 applies the principle of forced convectionto cool the PC board 64 and hence the control handle 16. As theintegrated circuits 80 on the PC board heat up during use of thecatheter, the heat generated is transferred to the heat exchanger 90. Asirrigation fluid transported by the proximal conduit 68 b flows throughthe heat exchanger 90, the heat transferred to the heat exchanger isfurther transferred to the fluid thereby cooling the heat exchanger.

As understood in the art, the heat exchanger 90 is configured todissipate thermal waste energy from the PC board 64 to the irrigationfluid from the reservoir 51 by maximizing surface area between the openspace in the control handle and the irrigation fluid, while minimizingresistance to fluid flow through the heat exchanger 90. The heatexchanger can take any suitable form, including a plate heat exchangeror a tubular heat exchanger, with parallel-flow, counter-flow, orcross-flow as desired or appropriate. The heat exchanger is constructedof any suitable material that is thermally conductive for optimal heattransfer. The material should also be biocompatible and suitable for ETOsterilization, including, for example, stainless steel or noble metalplated copper, such that contact between the irrigation fluid and theheat exchanger material does not compromise the fluid in terms ofsterility and biocompatibility when it exits from the ports in the tipelectrode and enters the patient's body.

Where the irrigation fluid is at room temperature, for example, rangingbetween about 20-25 C (or 68-77 F), the heat exchanger 90 can beexpected to raise the temperature of the fluid by about 5 degrees, toabout 25-30 C or (77-86 F). Since normal human body temperature is about37 C (or 98.6 F), there is little risk of introducing overheated fluidinto the patient, or of overheating the patient over the course of thecatheter procedure. However, if desired, temperature control over thefluid can be provided by means of a cooling unit 57, including, forexample, a radiator, a compressor, and an expansion valve, thatpre-cools the fluid from the reservoir by a predetermined amount beforeit enters the control handle and the heat exchanger so that thetemperature of the fluid exiting the heat exchanger and/or the controlhandle is generally predetermined before it exits the tip electrode andenters the patient's body.

In an alternate embodiment shown in FIG. 5, a heat transfer assembly 50a is configured as a closed system, wherein the coolant is recirculatedby the coolant transport network between one or more heat transferunits, such as IC heat transfer units 100, 200 and/or 250 provided onthe PC board 64, and a remote heat exchanger 92 connected via a coolantfeed conduit 69 b and a coolant return conduit 69 a. Coolant-cooledintegrated circuits are known in the art and are described in U.S. Pat.Nos. 7,400,502 and 5,360,993, the entire contents of which areincorporated by reference. FIG. 7a illustrates an embodiment of aconnector heat transfer unit (or hereinafter an IC heat transfer unit)100 of the prior art, which is depicted with a heat generating component101, such as an integrated circuit or chip, inserted into the connectorheat transfer unit 100. The IC heat transfer unit 100 may be of avariety of shapes and sizes, but these will be determined principally bythe size and electrical conductor configuration of the heat generatingcomponent and the motherboard (or PC board) to which the connector heattransfer unit will be coupled. All of the following embodiments of theIC heat transfer unit can be deployed in an application where the ICheat transfer unit is not mechanically attached to any type ofmotherboard and, it will be understood, that the IC heat transfer unitmay be electrically connected to the mother board in any suitablemanner. The IC heat transfer unit may be composed of any number ofmaterials but a lightweight, electrical insulating material isdesirable.

In FIG. 7a , the electrical conductors or pins 102 of the chip 101 areinserted into receptacles 104. A cavity 103 is disposed in the IC heattransfer unit 100 such that a surface of the cavity in thermally coupledto the surface of the chip 101. This surface of the cavity may becomposed of any good heat conducting material, such as copper, totransfer heat from the heat generating component to a coolant flowingthrough the cavity. The heat transfer unit 101 is configured with aninlet pathway 106 and an outlet pathway 108 for fluid entry and exitfrom the cavity. As understood by one of ordinary skill in the art, theconfiguration of the cavity and the pathways can be varied as needed ordesired to alter fluid flow efficiency.

The IC heat transfer unit pins 109 electrically connect the receptacles104 to the PC board, for example, by soldering. It will be appreciatedthat any suitable means may be used to connect the pins of chip 101 tothe PC board and the IC heat transfer unit is not limited to thereceptacles 104 and pins 109 described above. For example, the connectorheat transfer unit 100 may have a plurality of holes for pins 102 to beinserted into and through and then soldered to the PC board.

The surface of the cavity 103, thermally coupled to the heat generatingcomponent 101, is depicted as 110. The surface 110 may be comprised ofany good heat conducting material, such as copper. This surface 110 ispreferably coupled to the heat generating component 101 by means of athermal paste having good thermal transfer characteristics.Alternatively, the heat generating component 101 may be held in placewithin the connector heat transfer unit 100 and thermal coupling of thecomponent 101 to the surface 110 achieved by use of one or more clips,not shown, from the connector heat transfer unit 100 to the component101 or by a one or more clamp assemblies, not shown. In any case, it ispreferable to apply thermal paste to the coupling of surface 110 withthe component to insure maximum heat transfer. It should also beappreciated that the present invention encompasses many otherpossibilities for thermally coupling the component 101 to the surface110 including, but not limited to, application of mechanical force, suchas a clamping motion, to create a positive force between the component101 and the surface 110 and thus improve thermal conductivity.

The electrical conductors or pins 102 of most commercial heat generatingcomponents, such as microprocessors, for example, are typically coppercoated with precious metals. Thus, in addition to being good electricalconductors, they are also good heat conductors. Similarly, thereceptacles 104 and electrical conductors or pins 109 may be comprisedof similar materials with both good electrical and heat transfercharacteristics. The IC heat transfer unit 100 may then be comprised ofa material with good electrical insulation characteristics and good heattransfer characteristics to provide cooling and/or additional cooling ofthe chip 101. A wide variety of materials, such as a hard silicone, forexample, can be used for this purpose in the IC heat transfer unit 100.Specifically, heat from the chip 101 is transferred to the electricalconductors or pins 102. Some of this heat may be transferred from thepins 102, directly and/or indirectly through the receptacles 104 andpins 109, for example, to the IC heat transfer unit 100 and then on tothe cavity 103 where the coolant flowing there through will absorb someor all of this heat for dissipation. A thermal paste can be applied tothe electrical conductors or pins 102 to insure maximum heat transfer tothe body of the IC heat transfer unit 100 directly, or indirectlythrough the receptacles 104 and pins 109, for example. It should also beappreciated that pins 102 and the IC heat transfer unit 100 can bethermally coupled via other means including, but not limited to,application of mechanical force to create pressure in a clamping motion.

In yet another alternative for coupling the surface 110 to the chip 101,the surface 110 may be open or partially open allowing the coolant tocome into direct contact with the chip 101, which normally is encasedand protected by an IC pack (not shown) and thereby eliminating thethermal resistance of both the surface 110 and the thermal paste orother thermal connection medium used. In this situation, for example,the surface 110 could be in the form of a flange around the perimeter ofthe cavity 103. When the flange is coupled and sealed to the chip 101,the cavity is sealed and coolant will come in direct contact with thechip 101 without leaks or spills.

Referring now to FIG. 7b , a cover heat transfer unit 200 for the ICheat transfer unit 100 is depicted which provides additional cooling ofthe chip 101. The cover heat transfer unit 200 has many similarities tothe IC heat transfer unit 100, including a cavity 203. Entrances andexits for the coolant to and from the cavity 203 are provided by inletpathway 206 and by outlet pathway 208, respectively. The electricalconductors or pins 202 of the chip 101 are shown. Cavity 203 has asurface 210 which is thermally coupled to the chip 101.

Whenever possible, it is desirable to orient the heat transfer units 100and 200 so that the respective inlet is situated below the respectiveoutlet. This orientation allows the cooling system to take advantage ofconvective circulation of the coolant since heated coolant willnaturally rise and cooled coolant will naturally drop. In this manner,the thermodynamics of the coolant can assist forced circulation, by apump for example, and provide additional cooling of the heat generatingcomponents even after power is shut down.

A function of cover heat transfer unit 200 is to provide cooling to anadditional surface of the chip 101. As shown in the embodiment of FIG.7c , when a cover heat transfer unit 200 is used in conjunction with ICheat transfer unit 100 in forming a heat transfer module 250 to secureand cool a single chip, surface 210 is transferring heat from one sideof the chip to a coolant while surface 110 is transferring heat from anopposite side of the chip to a coolant. Use of the cover heat transferunit 200 then can provide dramatic increases in cooling power orcapacity when combined with the IC heat transfer unit 100.

The IC heat transfer unit 220 includes a cavity 223; a surface 230 ofthe cavity 223 thermally coupled to the chip 216; a plurality ofreceptacles or electrical contacts 224 to accept electrically theelectrical conductors 217 of the chip 216; and a plurality of pins orelectrical conductors 229, electrically connecting the receptacles 224to the PC board via, for example, by wave soldering.

The chip 216 may be held in place within the module 250 and thermalcoupling of the component to the surfaces 110 and 210 achieved by anynumber of methods. For example, one or more screws 212 threaded into oneor more mating receptacles 213 may be utilized. Alternatively, or inaddition, one or more spring clips, or any of a variety of mechanicalfasteners to create a clamping force, not shown, from the IC heattransfer unit 220 to the cover 200 and/or adhesives may be utilized. Inany case, it is preferable to apply a thermally conductive material tothe coupling of surface 230 with the component 216 and to the couplingof surface 210 to the opposite side of the chip 216 to insure maximumheat transfer.

In yet another alternative for coupling the surfaces 230 and 210 to thechip 216, either one or both of the surfaces 230 and 210 may be open orpartially open allowing the coolant to come into direct contact with thechip 216 and thereby eliminating the thermal resistance of both thesurfaces 230 and 210 and the thermal resistance of thermal paste orother thermal connection medium used. In this situation, for example,either or both of surfaces 230 and 210 could be in the form of a flangearound the perimeter of the cavities 223 and 203, respectively. When theflanges are coupled and sealed to opposite sides of heat generatingcomponent 216, the cavities are sealed and coolant will come in directcontact with the component on opposite sides there of without leaks orspills.

In operation, cooled coolant received from a heat exchange unit isapplied to inlet pathways 105 and 205. It flows through into thecavities 103 and 203. Heat from the chip 101 is absorbed into thecoolant and heats the coolant. The heated coolant then flows throughoutlet pathways 108 and 208 and is then directed back to the heatexchange unit for cooling. It will be appreciated and understood thatother methods of receiving the coolant, directing the coolant throughand out of the heat transfer module 250 may be utilized.

The heat transfer assembly in a closed or isolated configuration allowsfor more selection of a coolant since the coolant is not entering thepatient's body. A fluid with an ideal coefficient of variation (COV) foruse includes Propylene-Glycol. When used with an irrigated catheter,such a closed or isolated configuration allows for higher mass flowrates of coolant resulting increased convective heat transfer and adecrease in the thermal load to irrigation fluid preventing possibleloss in irrigation effectiveness at the tip electrode.

As understood by one of ordinary skill in the art, additional coolingmechanisms, such as air-cooled heat sinks or heat pipes for example (notshown), can be coupled to a free surface of the chip 101 to provide foradditional cooling, if desired. It is further understood that the handle16 and PC board may have any suitable shapes and sizes. As one ofordinary skill in the art, the location of the circuit board within thehandle can vary depending on the structures and components within thehandle, such as mechanisms for controlling deflection of theintermediate section 14 and various wires, cables and tubings thatextend through the control handle and distally along the catheter shaftand beyond.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. Any feature of any one embodiment can be used in anyother embodiment in the place of or in addition to other features. Forexample, although the first embodiment described herein features acatheter having an open system with a heat transfer assembly employingat least one heat exchanger mounted on the PC board and the secondembodiment features a catheter having a closed system with at least oneboard-mounted heat transfer module, the present invention includesembodiments where the catheter has a closed system with a heat transferassembly employing at least one heat exchanger mounted on the PC board(see FIG. 8), as well as a catheter having a open system with at leastone board-mounted heat transfer module (see FIG. 9). As understood byone of ordinary skill in the art, the drawings are not necessarily toscale. Accordingly, the foregoing description should not be read aspertaining only to the precise structures described and illustrated inthe accompanying drawings, but rather should be read consistent with andas support to the following claims which are to have their fullest andfair scope.

What is claimed is:
 1. An electrophysiologic catheter adapted for use ina patient's heart, comprising: a catheter body; a control handleproximal the catheter body, the control handle housing an integratedcircuit; a heat transfer assembly including a pump, a reservoircontaining a coolant, a heat transfer member, and a coolant transportnetwork providing coolant communication between at least the reservoirand the heat transfer member, wherein the heat transfer member islocated within the control handle to receive the coolant fortransferring heat from the integrated circuit to the coolant.
 2. Thecatheter of claim 1, wherein the coolant transport network is configuredas a closed network.
 3. The catheter of claim 1, wherein the coolanttransport network is configured as an open network.
 4. The catheter ofclaim 1, wherein the heat transfer member surrounds the integratedcircuit.
 5. The catheter of claim 1, wherein the heat transfer member isa heat exchanger.
 6. The catheter of claim 1, wherein the heat transfermember is an IC heat transfer unit.
 7. The catheter of claim 1, whereinthe heat transfer member is a cover heat transfer unit.
 8. The catheterof claim 1, wherein the heat transfer member is a heat transfer module.9. The catheter of claim 1, wherein the heat transport assembly includesa cooling unit and the coolant transport network includes a conduitreturning coolant from the heat transfer member to the cooling unit. 10.The catheter of claim 1, wherein the catheter includes a tip electrode,and an irrigation tubing delivering coolant from the heat transfer unitto the tip electrode.
 11. The catheter of claim 1, further comprising aheat exchanger remote from the control handle.